When an electrical or optical cable is being installed, it is generally made to pass through a duct intended for its mechanical protection. This is particularly useful in the case of an underground cable, which is not visible and therefore liable to be damaged.
The cables in question generally comprise conductors or fibers arranged in a common sheath which mechanically protects the assembly. They may include a mechanical reinforcement member which prevents any excessive elongation which would run the risk of breaking the conductors when the cable is being pulled through the duct.
To reduce the cost, while making handling easier, the duct is often made of plastic.
When an underground cable has just been installed, a test is made of the insulation between its conducting elements and earth so as to check that the sheath has not suffered during the installation operations. This is because a damaged sheath allows moisture to infiltrate, which could then damage the cable.
To check this insulation, a voltage is applied between the conducting elements and earth and if the measured insulation between the two is not perfect, there is electrical leakage and hence a risk of moisture getting in.
When the sheathed cable is placed in a duct, the presence of the latter causes difficulty as it introduces an additional insulation which precludes correct measurement of the insulation of the cable sheath.
However, it is necessary to detect any sheath defect from the outset so as to guarantee the desired reliability of the cable.
The problem that arises is how to check the integrity of the sheath of a cable installed in a protective duct and to measure any electrical leakage between the protective sheath and any internal electrical conductor, namely an electrical element, when there is one, or a mechanical reinforcement member, when there is one.
To solve this problem, the invention proposes a duct element intended to accommodate, on its internal wall, a sheathed electrical or optical cable in order to protect it, characterized in that the internal wall and the external wall of the duct element are electrically connected in order thereby to make an element for checking the integrity of the sheath of the cable.
Thus, the cable is set to the potential of the outside of the duct element and is therefore electrically accessible in order to allow a test of the insulation of the outside of the cablexe2x80x94a priori its insulating sheath - to be made.